1. Field of the Disclosure
The present disclosure relates to electronic devices, more particularly, to electronic devices that include conductive studs over bonding pad regions and processes for forming them.
2. Description of the Related Art
Solder bumps can be used to mount a die to a package as part of an electronic device. Solder bumps can include an under-bump metallization (“UBM”) layer and a solder layer. The solder bump can provide both physical and electrical connection between the die and the package. However, the coefficients of thermal expansion (“CTE”) of the die and the package may be different (“CTE mismatch”). Thus, as the electronic device changes temperature, the solder bumps can transfer stress between the die and the package to cause a failure such as die cracking. As such, a connection made with a more ductile bump material can be used across a wider temperature range than a connection made with a less ductile bump material providing the bump connection is sufficiently strong to attach the die and package.
As the die area decreases with succeeding process technology generations, features such as bonding pads and solder bumps also decrease in scale, which can increase current crowding. Electromigration increases with increasing current crowding, and can lead to bump failure. Current crowding also occurs when the current flow is from a material with a relatively lower resistivity to a material with a relatively higher resistivity, such as when current flows from the die to the package through the solder bump. Current crowding can be further exacerbated by a change in direction of the current flow, such as when a current moving along an interconnect level changes direction to flow through a solder bump.
One attempt to improve the situation is to add a copper pillar over the UBM layer. However, the copper is much stiffer than the solder that it replaces and can increase the likelihood of failure due to the CTE mismatch. Another attempt can be to use an Al capping layer over a Cu last metal layer. However, introduction of additional materials increases the complexity and expense of manufacturing by increasing the types of tools and processes required to form the electronic device.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments described herein. The use of the same reference symbols in different drawings indicates similar or identical items.